Not Applicable.
Not Applicable.
The present invention is directed to an apparatus for electrochemically processing a microelectronic workpiece. More particularly, the present invention is directed to a reactor assembly for electrochemically depositing, electrochemically removing and/or electrochemically altering the characteristics of a thin film material, such as a metal or dielectric, at the surface of a microelectronic workpiece, such as a semiconductor wafer. For purposes of the present application, a microelectronic workpiece is defined to include a workpiece formed from a substrate upon which microelectronic circuits or components, data storage elements or layers, and/or micro-mechanical elements are formed.
Production of semiconductor integrated circuits and other microelectronic devices from workpieces, such as semiconductor wafers, typically requires formation and/or electrochemical processing of one or more thin film layers on the wafer. These thin film layers are often in the form of a deposited metal that is used, for example, to electrically interconnect the various devices of the integrated circuit. Further, the structures formed from the metal layers may constitute microelectronic devices such as read/write heads, etc.
The microelectronic manufacturing industry has applied a wide range of thin film layer materials to form such microelectronic structures. These thin film materials include metals and metal alloys such as, for example, nickel, tungsten, tantalum, solder, platinum, copper, copper-zinc, etc., as well as dielectric materials, such as metal oxides, semiconductor oxides, and perovskite materials.
A wide range of processing techniques have been used to deposit and/or alter the characteristics of such thin film layers. These techniques include, for example, chemical vapor deposition (CVD), physical vapor deposition (PVD), anodizing, electroplating, and electroless plating. Of these techniques, electrochemical processing techniques (i.e., electroplating, anodizing, and electroless plating) tend to be the most economical and, as such, the most desirable. Such electrochemical processing techniques can be used in the deposition and/or alteration of blanket metal layers, blanket dielectric layers, patterned metal layers, and patterned dielectric layers.
One of the process sequences used in the microelectronic manufacturing industry to deposit a metal onto semiconductor wafers is referred to as xe2x80x9cdamascenexe2x80x9d processing. In such processing, holes, commonly called xe2x80x9cviasxe2x80x9d, trenches and/or other micro-recesses are formed onto a workpiece and filled with a metal, such as copper and/or a copper alloy. In the damascene process, the wafer is first provided with a metallic seed layer which is used to conduct electrical current during a subsequent metal electroplating step. If a metal such as copper is used, the seed layer is disposed over a barrier layer material, such as Ti, TiN, etc. The seed layer is a very thin layer of metal, such as copper, gold, nickel, palladium, etc., which can be applied using one or more of several processes. The seed layer is formed over the surface of the semiconductor wafer, which is convoluted by the presence of the vias, trenches, or other recessed device features.
A metal layer is then electroplated onto the seed layer in the form of a blanket layer. The blanket layer is plated to form an overlying layer, with the goal of providing a metal layer that fills the trenches and vias and extends a certain amount above these features. Such a blanket layer will typically have a thickness on the order of 10,000 to 15,000 angstroms (1-1.5 microns).
After the blanket layer has been electroplated onto the semiconductor wafer, excess metal material present outside of the vias, trenches, or other recesses is removed. The metal is removed to provide a resulting pattern of metal layer in the semiconductor integrated circuit being formed. The excess plated material can be removed, for example, using chemical mechanical planarization. Chemical mechanical planarization is a processing step which uses the combined action of a chemical removal agent and an abrasive which grinds and polishes the exposed metal surface to remove undesired parts of the metal layer applied in the electroplating step.
The electroplating of the semiconductor wafers takes place in a reactor assembly. In such an assembly, an anode electrode is disposed in a plating bath, and the wafer with the seed layer thereon is used as a cathode. Only a lower face of the wafer contacts the surface of the plating bath. The wafer is held by a support system that also conducts the requisite electroplating power (e.g., cathode current) to the wafer.
Several technical problems must be overcome in designing reactors used in the electrochemical processing of microelectronic workpieces, such as semiconductor wafers. One such problem relates to the formation of particulates contamination, gas bubbles, etc., that form at the surface of the anode (or, in the case of anodization, both the cathode and anode) during the electrochemical process. Although such problems exist in connection with the wide range of electrochemical processes, the discussion below focuses on those problems associated with electroplating a metal onto the surface of the microelectronic workpiece.
Generally stated, electroplating occurs as a result of an electrochemical reduction reaction that takes place at the cathode, where atoms of the material to be plated are deposited onto the cathode by supplying electrons to attract positively charged ions. The atoms are formed from ions present in the plating bath. In order to sustain the reaction, the ions in the plating bath must be replenished. Replenishment is generally accomplished through the use of a consumable anode or through the use of an external chemical source, such as a bath additive, containing the ions or an ion-forming compound.
As the thin film layer is deposited onto the cathode, a corresponding electrochemical oxidation reaction takes place at the anode. During this corresponding electrochemical reaction, byproducts from the electrochemical reaction, such as particulates, precipitates, gas bubbles, etc., may be formed at the surface of the anode. Such byproducts may then be released into the processing bath and interfere with the proper formation of the thin-film layer at the surface of the microelectronic workpiece. Furthermore if these byproducts are allowed to remain present in the processing fluid at elevated levels near the anode, they can affect current flow during the plating process and/or affect further reactions that must take place at the anode if the electroplating is to continue. For example, if copper concentrations are allowed to increase excessively, copper sulfate will precipitate due to the common ion effect. In order to reduce and or eliminate this problem, electrolyte flow near the anode is maintained at a sufficient level to allow mixing of the dissolved species in the electrolyte.
Such byproducts can be particularly problematic in those instances in which the anode is consumable. For example, when copper is electroplated onto a workpiece using a consumable phosphorized copper anode, a black anode film is produced. The presence and consistency of the black film is important to ensure uniform anode erosion. This oxide/salt film is fragile, however. As such, it is possible to dislodge particulates from this black film into the electroplating solution. These particulates can then potentially be incorporated into the deposited film with the undesired consequences.
One technique for limiting the introduction of particulates and/or precipitates produced at the anode into the plating bath, has been to enclose the anode in an anode bag. The anode bag is typically made of a porous material, which generally traps larger size particulates within the anode bag, while allowing smaller size particulates to be released external to the bag and into the plating bath. As the features of the structures and devices formed on the microelectronic workpiece decrease in size, however, the performance of the structures and devices may be degraded by even the smaller size particulates. Furthermore, while the use of an anode bag will restrict the larger particulates from traveling toward the cathode and contaminating the plating surface or affecting the plating process taking place at the cathode, the anode bag will also trap the larger particulates within the proximity of the anode creating elevated levels of these byproducts, which may limit the forward electrochemical reaction taking place at the anode. Still further, the larger particulates can eventually block the porous nature of the anode bag and ultimately restrict even the regular fluid flow.
The present inventors have recognized the foregoing problems and have developed a method and apparatus that assists in isolating byproducts that form at an electrode of an electrochemical processing apparatus to prevent them from interfering with the uniform electrochemical processing of the workpiece.
A reactor for use in electrochemical processing of a microelectronic workpiece is set forth and described herein. The apparatus comprises one or more walls defining a processing space therebetween for containing a processing fluid. The processing space includes at least a first fluid flow region and a second fluid flow region. A first electrode is disposed in the processing fluid of the first fluid flow region while a second electrode, comprising at least a portion of the microelectronic workpiece, is disposed in the processing fluid of the second fluid flow region. Fluid flow within the first fluid flow region is generally directed toward the first electrode and away from the second electrode while fluid flow within the second fluid flow region is generally directed toward the second electrode and away from the first electrode. Depending on the particular electrochemical process that is to be executed, the first electrode may constitute either an anode or a cathode in the electrochemical processing of the microelectronic workpiece. The foregoing reactor architecture is particularly useful in connection with electroplating of the microelectronic workpiece and, more particularly, in electroplating operations that employ a consumable anode, such as a phosphorized copper anode.
In accordance with one embodiment of the invention, the reactor comprises at least one pressure drop member disposed in the processing fluid of the processing space in an intermediate position between the first and second fluid flow regions and the first and second fluid flow regions are adjacent one another.
The pressure drop member may comprise a permeable membrane that is disposed over an open end of a cup assembly wherein the membrane is permeable to at least one of the ionic species in the processing fluid. The cup assembly may comprise an electrode housing assembly having an inverted u-shaped lip, and an outer cup assembly. In accordance with a further enhancement of this embodiment, the cup assembly further includes at least one outlet tube having an opening, which extends into the space within the inverted u-shaped lip of the electrode housing assembly. The outlet tube provides a path for processing fluid, gas bubbles, and particulates to exit the cup assembly, while the pressure drop member restricts movement of the same into the second fluid flow region of the cup assembly.
A method for processing a microelectronic workpiece is also set forth. In accordance with one embodiment of the method, a processing space containing processing fluid is divided into at least a first fluid flow region and a second fluid flow region. A first electrode is located within the processing fluid of the first fluid flow region and a second electrode comprising at least a portion of the microelectronic workpiece is located within the processing fluid of the second fluid flow region. A fluid flow of the processing fluid is generated within the first fluid flow region that is generally directed toward the first electrode and generally away from the second electrode while a fluid flow of the processing fluid within the second fluid flow region is generated that is generally directed toward the second electrode and generally away from the first electrode.